Provided by: libperl-critic-perl_1.130-1_all 
NAME
Perl::Critic::CORE_DEVELOPER - Hints for working on the Perl::Critic core.
DESCRIPTION
This document is a grab-bag of notes for those who are working on the underpinnings of
Perl::Critic. They are intended to be informative, but unfortunately can not really be
considered authoritative. It is in the nature of the task being described that the user of
this document will end up working out the details for him- or herself based on the actual
work being performed. Caveat lector.
BECOMING A CORE DEVELOPER
Here are my thoughts on how to get started. Note that the steps are not numbered because
I'm not sure there is a clear order to them. The items with two stars in front of them are
from the mailing list; the ones with one star are my opinion. Although sometimes I have
felt it helpful to comment on the two-star items, just to make things thoroughly unclear.
* If you're unsure of yourself, install Perl::Critic, then download the source and rummage
around in it.
** Subscribe to the developers' mailing list. There are instructions in "EXTENDING THE
CRITIC" in Perl::Critic. The commits mailing list is another good one.
** If you are working on a GitHub issue, you should update the ticket to say that you are,
to keep other people from duplicating your effort.
* I personally would update GitHub at the point I was reasonably confident I could hack
it, just to prevent myself from having to update GitHub again in a week or so saying
"oops, bit off more than I could chew." But that's me talking.
* Development requires using Module::Build rather than ExtUtils::MakeMaker. In other
words,
$ perl Build.PL
$ ./Build
$ ./Build test
* You need to run the suite of author tests by running
$ ./Build authortest
(but not 'make authortest', which is one of the reasons you should start with Build.PL
rather than Makefile.PL) These should run cleanly before you declare your work done. My
advice, though, is not to worry about them until your code is functionally correct.
Modules required for authortest
The authortest requires a bunch of modules above and beyond those required to run
"Perl::Critic". The list probably depends on which "Perl::Critic" you are testing, so the
following should not be considered definitive. You need the following in addition to all
optional modules for Perl::Critic itself.
Devel::EnforceEncapsulation
Perl::Critic::More
Test::Kwalitee
Test::Memory::Cycle
Test::Perl::Critic
Test::Pod
Test::Pod::Coverage
Test::Without::Module
You can find out what the optional modules are by looking at
"recommended_module_versions()" in inc/Perl/Critic/BuildUtilities.pm.
In the absence of "Test::Memory::Cycle", the relevant tests are simply skipped. In the
absence of the other modules, the tests die horribly. Of course, either way they do not
get run, so the difference is mainly one of aesthetics.
Under Perl 5.12 and above, Devel::Cycle 1.11 needs to be patched to handle a "Regexp" as a
first-class Perl object. See <https://rt.cpan.org/Public/Bug/Display.html?id=56681> for
the details.
ADDING A GLOBAL CONFIGURATION ITEM
Perlcritic handles global configuration items and command line options in very similar
ways. These notes will cover adding both a global configuration item and a corresponding,
same-named command option. These notes can not, of course, cover implementing the
functionality of the new item, just the mechanics of getting the item into Perl::Critic.
Naming Conventions
All names are lower-case, except for the names of constants (if any), which are upper-
case. When a name contains multiple words, dashes will be used to separate the words in
the configuration item name and the command line option, and underscores will be used in
the accessor and attribute value names, and constant names if any.
For example, if "new item" is being added, the configuration item is "new-item", the
command option is "--new-item", the accessors are "new_item()", and the value of the
attribute will be stored in "$self->{_new_item}". If there are constants involved, their
names will start with "NEW_ITEM_". These names will be used in the following discussion.
Implementation
There are several files that must be modified to get your new configuration item and/or
command line option.
lib/Perl/Critic/Utils/Constants.pm
If there are manifest constants connected with your implementation they go here. You may
well at least have a
$NEW_ITEM_DEFAULT
to define. All the constants for your new item must be exported, and should be exported
not only individually but all together with export tag
new_item
lib/Perl/Critic/Command.pm
If your new item is a command option, its Getopt::Long specification must be defined in
"_get_option_specification()". If your new configuration item does not have a
corresponding command option, you do not need to make any changes to this file.
lib/Perl/Critic/OptionsProcessor.pm
If your new item is a global configuration item, you need to add the code to handle it
here. Specifically:
You must add code to the "_init()" method to store the value of your item as an attribute
value, defaulting it if necessary. Using our naming convention, a single-valued item would
be stored like this:
$self->{_new_item} = dor(delete $args{'new-item'},
$NEW_ITEM_DEFAULT);
If the item has synonyms (e.g. both 'color' and 'colour' meaning the same thing), the
"dor()" call must check for all of them. If the item took a list of values, they would be
parsed apart and stored as an array reference.
You must also add and document an accessor for your new item. This would look something
like this:
sub new_item {
my ($self) = @_;
return $self->{_new_item};
}
In the case of multi-valued items, the accessor must return the array reference, so the
above specimen code works in that case also.
Note that no validation is done here -- this class is simply a bridge between the physical
.perlcriticrc file and Perl::Critic::Config, which is where the action is.
If your new item is a command option without a corresponding global configuration item,
you do not need to modify this file.
lib/Perl/Critic/Config.pm
You must write a "_validate_and_store_new_item()" method to validate and store the value
of the new item. The signature of this method depends on the details of your new item, but
it must include at least the value of the item, even if there is no corresponding global
configuration item. If it is possible to get validation failures, it will also need an
errors object to add the validation exception to. Because the details vary, the best way
to proceed is probably to find a method similar to the one you want to write, and
implement from there. The "_validate_and_store_top()" method is a reasonable starting
point for an item having a single value. The validated value needs to be stored in
"$self->{_new_item}".
You must call "_validate_and_store_new_item()" in the "_init()" method.
You must write and document an accessor method for the value of the new item. The typical
accessor method for a single-valued item is
sub new_item {
my ($self) = @_;
return $self->{_new_item};
}
but the accessor for a multi-valued item must return a list:
sub new_item {
my ($self) = @_;
return @{ $self->{_new_item} };
}
Last, you must document the item itself.
lib/Perl/Critic/ProfilePrototype.pm
If your new item has a corresponding global configuration item, you must update the
"to_string()" method to include the item in the string. Your implementation of the item
must be such that the generated string is the same as the input string for the item,
except for whitespace.
If your new item has no corresponding global configuration item, you do not need to change
this file.
bin/perlcriticrc
If your new item has a corresponding command option, you must document it here. If it does
not, you do not need to change this file.
examples/perlcriticrc
If your new item has a corresponding global configuration item, you must add it here. If
it does not, you do not need to change this file.
Testing
The following test files must be considered for modification:
t/00_modules.t
t/01_config.t
t/01_config_bad_perlcritic.t
t/04_options_processor.t
t/07_command.t
t/10_user_profile.t
t/16_roundtrip_defaults.t
Depending on your new item, you may not need to change all of these, but you should at
least review them. Depending on what your new item actually does, other test files may
need to be modified as well.
DEPRECATING AND REMOVING A PUBLIC SUBROUTINE OR METHOD
This is something to be done cautiously. The code in question may only exist to serve
Perl::Critic, but if it is documented as public it may well be in use "in the wild",
either in add-ons to Perl::Critic or by users of Perl::Critic.
Before deprecating public code, the potential deprecator must discuss the issues on the
Perl::Critic developers' mailing list. There are instructions on how to subscribe to this
list in "EXTENDING THE CRITIC" in Perl::Critic.
Once agreement is reached, the technical details of the deprecation are fairly simple.
You must insert something like the following in the code to be deprecated:
warnings::warnif(
'deprecated',
'Perl::Critic::Utils::foo() deprecated, use blah::foo() instead.',
);
You should have the deprecated subroutine delegate its functionality to the new
subroutine, if that is practical (it may not be).
You must update the documentation to say that the old code is deprecated, and what the
replacement is.
After the old code has been deprecated for a couple production releases, it can be
removed.
AUTHOR
Thomas R. Wyant, III wyant at cpan dot org
COPYRIGHT
Copyright (c) 2009-2011 Thomas R. Wyant, III
This program is free software; you can redistribute it and/or modify it under the same
terms as Perl itself. The full text of this license can be found in the LICENSE file
included with this module.